powell



W. T, POWELL.

TELEPHONE EXCHANGE svsrem.

APPLICATION FILED JULY 24, 19-16. 1,308,553. Patented July 1, 1919,

4 SHEETS-SIIEH w. T. POWELL. TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED JULY 24,1916.

Patented July 1, 1919.

4 SHEETS-SHEEI 2.

W. T. POWELL.

TELEPHONE EXCHANGE SYSTEM. APPLICATION FILED JULY 24. I916.

1,308,553. Patented July 1, 1919.

4 shins-sun a Hiram-25y W. T. POWELL.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION mu) mu! 24. me.

1,308,553. Patented July 1, 1919.

5. ,l lgusnfaz" $2 2 HZZbPnEy UNITED STATES PATENT OFFICE.

WINFRED '1'. POWELL, OF CHICAGO, ILLINOIS, ASSIGNOR TO AUTOMATIC ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

TELEPHONE-EXCHANGE SYSTEM.

Specification of Letters Patent.

Patented July 1, 1919.

Application filed July 24, 1916. Serial No. 110,925.

To all whom it may concern:

Be it known that I, lViNrnnn T. POWELL, a citizen of the United States of America, and a resident of (hicago county of Cook, and State of Illinois, have invented certain new and useful Improvements in Telephone- Exchange Systems. of which the following is a specification.

My invention relates in general to im provements in telephone cxchan c systems and is concerned more particular] y with those systems in which the telephonic connections are established through the medium of automatic selector and connector switches.

Systems of the foregoing character are naturally divisible into two great classes, automatic and semi-automatic, the distinc tion lying in the method of controlling the automatic switches. In the so-calledfull automatic systems each substation instrument is provided with an impulse sender or calling device by means of which the subscriber is enabled to control the central oflice switching mechanisms to establish connections entirely independent of manual assistance at the exchange. On the other hand, in semi-automatic systems, the substation instruments WQ of the ordinary manual type, and a subscriber, when making a call, is first connected with an operator, who controls the automatic switches thereafter to establish the connection in accordance with directions supplied by the calling subscriber.

It is the chief object of my invention to provide a telephone exchange system in which it is a matter of indifference whether any particular substation is provided with a calling device or not. In my improved system, a calling line, whether manual or automatic, is connected by a preliminary trunking operation responsive to the removal of the receiver with the first of the numerical selector switches through the medium of which the connection is to be established. Immediately afterward. it the calling line is equipped with a manual substation only, the call is trunked to an operator who controls the automatic switches to establish the connection in the well known manner. In case. however. the cal ing line is equipped with an automatic substation, the latter trunking operation is not performed and the calling subscriber himself controls the establisln ment of his connection. To accomplish the foregoing, apparatus provided associated with the preliminary trunking equipment which is able to discriminate between automatic and manual calling, lines, as will be fully explained hereinafter.

A further feature of my invention relates to the preliminary trunking apparatus. Primary and secondary tinder switches are employed which mechanically are of the well known single rotary type but whose circuits are modified in certain details which will be explained, with a view to securing great rapidity in extending a walling line to an idle selector switch.

Still another feature of my invention rclates to a combined line and cut-oil' relay. By a peculiar circuit arrangement and relay construction I am able to dispense with the usual line and cut-oft relays and provide instead a single r :lay individual to each line which performs the functions of both a line and a cut-off relay.

These and other features will be explained more in detail in the description which is to follow reference being bad to the accompanying drawings. For a clear understand mg of the drawings Figures 1. 2. and 2'5 should be arranged in order with the lines thereof in alincment. and Fig. 4 should be placed beneath Fig. 3 with the lines at the top of Fig. 4 in alincment with the linesat the. bottom of Fig. \Vhen properly arranged the drawings show diagranunatically the essential parts of a complete system cmbodying the principles of my invention.

It has been thought advisable to show a portion of the apparatus in operated posh tion whereby a connection has been cstab lished between a calling manual substation (Fig. 1) and a called automatic substation (Fig. 3). The said connection has been established through the medium of the primary and secondary finder switches C and I) the selector switch E (Fig. 2). and the connector switch F (Fig. 3). The opera tors equipment by means of which the establishment of the connection was controlled is shown in the lower half of Fig. 3 and in Fig. 4. while the means by which the call was extended to the operators position comprises the relay equipment H and the primary and secondary line switches M and N (Fig; 2). In Fig. 5 is shown in detail the spring combination of one of the subscribers individual line relays.

Referring now to Fig. I, the ananual substation A comprises; the usual common hattery arrangement in which the transmitter and receiver are connected in series. The line Ponduetors 1:2 and 13 have allotted to them atthe exchange it combinml line and out-oti relay 1-1: sets of multiple contacts in the huniis of r. plurality of finder switches, one of which sets is indicated by retcrenco characters 27-30 inclusive; and u SPtmO-E multiple contacts (not shown} in the hunk of each connector such us connector F Fig. 3). which has access to the group of lines of which the line of substation Ais one. The normal conductors so, mid 37 extene to these hitter sets of contacts.

The relay 14 comprises two windings one of which. the Winding 15, oi high resist wire and few turns. hcing prefer-old of German silver Wire. Referring to the dctiiiled showing of Fig. 5, when the two Wind ings are energized. in series the illllllltlll'e is attracted with suiiicient force to bring the Contact spring 21 against the bushing by which the springs 17 and 19 are controlled thereby separating the said spring 21 from spring 2:2. The springs 17 and 19, however, are quite stili' and consequcntiy are not separruted from their resting contacts 13 and :31). 'hen the winding 16 is energized alone the armature fully attracted.

It has been mentioned before that the subserihers lines may be equipped either with manual or automatic substations indiscriminnteiy and there is shown, accordingly, an automatic substation A provided with line conductors 1:2 and 13' which terminate at t1 e. exchange in individual line equipment exactly like that already described in the case of the line of substation A. Being :in automatic substation, the substation A is provided with the usual calling device or impulse sender which as shown herein diagrammatically comprises a pair of impulse springs .3 and 3 controlled hy the impulse wheel 4 through the nuuliun: ot' a finger hole iliul (not shown). An impulse sender suit able for the purpose is shown in British patent to H. U. S. Dicker. #291554 of Hill).

For culling purposes the suhscrihcrs linci are prcierzilily divided into hundred lino groups. correspondin to the I: parity of it connector switch. lunch group of lines is served by a group of selector swillilns, usually ten in number. one of these selectors being shown at E (Fig. 2). As. is clzslonnuy in finder switch systems. curh selector switch is prewiiicd with n prinuiry tinder switeh by which it only he connected with n calling iine. For example. the selector switch it provided with the prinnirv finder switch C. In order to decrease the HHlXlIHlml number or" conl'ncts over which :1 primary iindor may he required to hunt to locate a rolling line. I do not give these primary finders direct arc-ens to calling lines hut instead interpose lesser groups ol seooudury tinder switches, one of which swit h-cs i indicated or reference clnirucler l ln cnrrying out this plan, n h'nni'lreil line group may he, sub-divided into four twenty-tire line groups. the lines of eeich sub-group lining served li six; seeonihir tinder swiwlu-s. The seconijli ry find crs ot' the four suboops. twenty-four alto gethcr, arc :IHCQH. to the ten primary tinder switches eorrespoiuling to the ten selector switches serving the main group. By the toregoin' arrangement, ouch tinder switch is requi .cd to hunt over ii maximum of twenty-fire lines (twenl-ytour in the ease of the primary finders) iusteud of one hundred lines; as would lie the case il priinui'y finders alone were used.

)lcchuuicullv the tinder m\\ii.fil*S shown herein are of the Well known single rotary type. in which the wi 'iers have no normal position. A switch o'i' suitnhle inechnniczil construction is shown in the patent to lcnwnl. #i.l(l7,153. The circuits by which the linder switches are controlled, howev r, are heiiereil in he new in certain details which will he tully described in the detailed speciliriuion which is to tollou".

The seiector switch E (Fig. 2) is oi the. general typo ol' sele tor switch disclosed in l h. Letters lntent #815,2l2l, granted Mnroh 125, 1906, to Keith. Brink-son. mid Erickson; the side switch and priviile lung not. however, lining omitted and the circuits being modified to eiulhle the switch to operate in :1 system in which the impulses are delivered over the two sides ot the line in series. A selector switch of the foregoing type, in. is well known. only be, operated in nusponwto thc first digit of :1 culled nuniher to select one 1? :i. niunher of main groups into which the lines ot the exchange. are divided. For this purposethe selector ll. in common with othorsinlilnrsclec{ors.1nn y he given n ress to :1 number of groups of trunk lines. the iron]; lines of ouch group heiug extruded to :i group of connector switches.

)ne of those lrnnli lines is shown extruding to the connector l (Fig. It). which is ol the general typo ol connector su'ilrh dis l'ioseil in i H. licilcrs lntcnt #515376 granted lvlurch l3. Mon. to hcilli. Erickson, and l lriclcsonz living. lunrcrcr. oi the pun lir'ulur iypc iiisrloscd in l S. Letters Patent .#II.-.Jtll. reissued April 31. 1015, to Frank Nou'torlh. A rounecl'or switch of the toregoing typo nnrwhe given nccr to :1 group of one hundred suhscrihcr e lines as has been previously lllillilflllttl, and is opernhle in rcspouse to the two lust digits of :1 culled nuuihcr to establish oonnoct ion with un iinc in the group. I

time ol' the linen to whimi the connector F has across is shown extending to the sulostw tion A which is similar to the substation A already described. and is provided with similar individual line ,equipment at the exchange.

Before proceeding further it should he mentioned that while I have shown the first selector switch E as having direct access to the connector switches, this will be true only in a small exchange. In larger systems sec end and third selectors may be interposed.

7 H operates to direct the call to an operarcs 'ionding spring clips or jacks 123 tors position. Since the apparatus H must be able to discriminate between automatic and manual lines it is evident that the two kinds of line must have some distinguishing feature. With this object in view each individual line relay is provided with two terminals. indicated in the case of line relay 14 (Fig. I) by reference characters 24 and 25. between which there is or is not connected a resistance, such as resistance 26, depending on whether the associated line is equipped with a manual or automatic substation. The effect of this resistance in controlling the operation of the relays H will be fully explained hereinafter.

It may happen that certain groups of lines may be equipped throughout with automatic substations in which case the apparatus H associated with those groups may be dispensed with. For convenience I have contemplated mounting each group of relays H on a bracket provided with spring clip terminals which. when the equi nnent is installed, will engage cor- 128. inclusive. \Vhen the relay equipments associated with a certain group of lines are to he removed. it is only necessary to dismount the several relay brackets, and connect the terminals 123. 124. and 1251. respcctively. with the terminals 126. 127. and 1:48, by means of jumpers. This feature is especially valuable where an existing manual or semi-automatic system is to he gradually changed over to a full automatic system.

The primary and secondary rotary line switches M and N are of the same general construction mechanically as are the linder switches and I) already described, although the circuits are simplified and changed in ccrtain details which will be xplaincd in order to take -a re of the somewhat different functions which these switches perform.

The trunkingarrangement of the primary and secondary line switches is in accordance with the usual practice. A plurality of primary line switches similar to the line switch M are given common access to a group of t\\'cnty-five secondary linc switches similar to the line switch N. The secondary line switches have common access to a group of twenty-five trunks which extend to operators positions. ()ne of these is shown extending from the bank contacts l9-l197, inclusive. to the operators equipment indicated collectively by reference character 0 (Fig. 3). It is considered best to have three trunks terminate in each opcrators position. although the number may be varied if desired. Means is provided whereby when a. call is received over one trunk the others terminating in the same position are made busy until after the call is handled by the operator. An individual busying key K is also provided.

In Fig. 4 there is shown an operator's impulse sending equipment which is individual to the trunk line terminating in the equipment 0 (Fig. 3). The equipment. shown in Fig. l is taken from the co-pending application of John G. Blessing. Serial #740,953 and consequently no detailed description will be given herein. It will sntlice to say here that upon receiving a call the operator depresses in rapid succession the keys which correspond to the digits in the desired number. after which she depresses the starting button S. \Vhen the operator depresses the digit keys the sender automatically registers the number wanted and thereafter, in response to the operation of the starting button. proceeds to transmit to the automatic switches the required series of impulses to control the establishment of the connection, all of which will appear nnn'c clearly from the description of the opcration which will presently be given.

\Vhile I have shown throughout the drawings a plurality of batteries it is to he understood that there is preferably but one buttery having its positive pole grounded. The auxiliary apparatus shown in association with the connector F (Fig. and comprising the ringing current generator (ien. the interrupter I. and the busy signaling machine Q. are of the usual type and perform the same functions as the same named pieces of apparatus in other automatic exchanges.

Having briefly described the apparatus. l avill now proceed to a description of the op cration thereof. For the purposes of this explanation it will he assumed that the sill)- scriber at the manual substation A (Fi 1) wishes to obtain connection with the snhscribcr at the automatic substation A (Fig. 3) this being the complete circuit connection shown in the drawings. Afterward it will be explained wherein the operation. of the equipment ditl'ers when the subscriber at the automatic substation A (Fig. 1) attempts to establish the same connection. A great part may .1 Hm manual {320 minimum Immw 55 w tho Insv vi-M121 1 mf' rainy T m and uh n-nupiutes :Ln

is bait liil net 52 to battery B Relay 50 is of high resistance so that the rotary magnet 52 15 not affected. Upon energizing, relay 50 shifts its contact springs to the position shown with the result that the wiper 32 is disconnected by means of armature 61 from the circuit extending to the rotar magnet; a circuit for the cut-off relay 14 is prepared at armature (i5; and the starting wire 43 is disconnected by means of armature 66 from the line inlay 51 and, upon the denergization of the line relay, is connected to the starting wire 44 of the next finder switch. At the same time that relay 50 is operated, the line switching relay 75 of the finder switch C is energized over the following circuit: ground at. G, armature 107 of relay 105, contact 108, common conductor 85, armature 82 of relay and its front contact, winding of relay 7:). armature 83 of rotary magnet 77 and its back contact, and winding of rotary magnet 77 to battery B. Relay 75, like relay 50, is of high resistance. Upon energizing, relay disconnects the wiper 102 from the operating circuit extending to the rotary magnet 77 by means of armature 84; disconnects the starting wire 45 from the line relay 70 and, upon the dei uergization of the line relay. connects it to the starting wire 40 of the next tinder switch; prepares a holding circuit for itself by means of its armature 00: and by means of armatures )2 and 93 extends the wipers 101 and 101i to the denble-wound line relay 300 of the selector E.

The said line relay 300 is now energized over the following circuit: ground at. G. lower winding of line relay 300. normally closed contact of relay i302, terminal 127, conductor 151, resting contact and arma tnrc 123C) of relay 1230. terminal 124, conductor 121. contact 93, wiper 104, bank contact 08, wiper 3-1, bank contact 30. line conductor 12, to and through substation A, line conductor 13. bank contact 27, wiper 3]. bank contact 95, wiper 101, armature 02, contact 91, conductor 120, terminal 123. armature 134 01'' relay 130 and resting contact, conductor 1525. terminal 120, normally closed contact of relay 302. and upper winding of line relay 300 lo battery B. Upon attracting its armature, the line relay 300 closes a. circuit for the slow-acting relay 2'01. which relay. upon energizing. prepares a circuit for the vertical magnet 304 in the usual manner. An additional result is the closure of a holding circuit for the relays 75 and 50 of the finder switches (l a1 1d D and the cut oil relay 14 which may be traced as follows: ground at G". contact 308, armature 30!), terminal 128. conductor 15."), winding of relay 130, terminal 125, conductor 122. wiper 103. bank contact 97. contact 01. armature 5 of relay F10, wiper 33. hank contacl 20. terminal 24, and winding 16 of cut-off relay 14 to battery B. It will be seen that a branch of the above circuit extends by way of the winding of relay 75 and the rotary magnet 77 to battery B, while a second branch extends by way of the windin of relay 50 and the rotary magnet 52 to battery B. The line relays 51 and 76 are made slowacting so to retain their armatures until after the holding circuit above traced has been completed.

Upon the completion of the holding circuit the cut-off relay 14 fully attracts its armature thereby disconnecting the line conductors 12 and 13, respectively, from the starting relay 39 and from the winding 10; and also again connecting ground G to the test contact 28 to protect the line against seizure by another tinder switch. The finder switch I) is protected in a similar Way against seizure by another primary finder switch by the connection of ground G with test contact 96 upon the deiinergization of line relay 5 1. A third branch of the holding circuit extends via conductor 35 to multiple test contacts in the banks of the connector switches which have access to the line of su bsl'ation A. The relay 130 (Fig. 2) is of very low resistance so that these test contacts are brought sutliciently near to ground potential to render the said line busy.

'losnm up the preliminary trunking operation briefly. it will be seen that upon the initiation of a call a primary finder switch and a secomlary tinder switch are started simultanwusly. it will be seen further that the first switch to locate the contact set for which it is hunting waits until the. other finder has stopped. when the switching rclays ol both finders pull uptogether. It is understood. ot' coursmthat in case one of the finder switches already has its wipers in engagcment with the contact set to be connected with. no rotation of its wipers will take place.

The foregoing operations. resulting in the extension of thecalling line to the selector 1C. have taken place in response to the remoral of the receiver at substation A. Since substation A is a manual substation it will now be necessary to trunk the call to an operator. This operation, as has been previously mentioned. is started or controllcd by the apparatus 11' (Fig. 2). The switching relays 75 and 50 of the finder switches (l and l) and the winding 1(3 of cut-oil relay 14 being all of high resistance. they would not permit sullicienl current to fl w over the holding circuit to energize the low resistance relay 130 of the relay group ll were it not for further provisions. The object of the resistance 21': across the terminals 2i and 25 of lhe cul oil relay ll now becomes apparent. The opcraliou of the relay 130 depends on the provision or omission of this resistance, or in other words, relay 130 is a marginal relay which 'oper iii! intent, rfispct-tively, with contat'ts IT E ITT, inclusive. Also thv. line switching relay 161, living no lungm' sl'iul't-vircuitetl, will ener- ,Lfilt' with the full ng results: By the tHUttttlUH (If aumutilrv 166 the pri ate xipvi' ii] is shifted to the ground side of the rehrylfll; tnnmture 1H5 mnnvcts mntlucltii E5: to the wipti' 172; and finally lay i'itUEEllH tat miniatures 1632\l1tl 10L the lin min tlnvt'tim 150 and 1:31 are disconnected, Ti,- rtpt-t-titvly. from the linu relay 160 and from gllititlllti (1; anti :tl't (,Xitflldfll Ly way of wipvm lit) and 173, and bank contacts 174 11ml 1?? to the llllt relay 186 of the secondary switch N mid to ground G. The line l'vln v 184i in mm PtttFgIlZttl river thn pr;- winnsly (leis ml vim-nit including the :-;nhst-rilitrrl; loop and pui'ftn'ma the stunt: fm1cnuns as lmiil ver: tlLrifllll'Pa, in the. (3:152 0% lllt' linci't'ltty i 'll of tin: primaiy switch M. A Immt'h til the met" cing vim-int of relay 3*?) NXlttHlH i lliilt wire jllntfillflfili 134 215* way til ltwi. t'hltiilt'l li'ii, itrl'i wiper l' 'i, armature itit mi t working mutant, winding of line .-:\\'in-l|ing relay ltli. :irmutln'n of mtary mag net 1152 tlllll l'lit' winding of the Said mtiu'y ni-tQfttt-t to inttt't-ry ii. The almve holding (lt" lil is {"Sl'lllillhifltl before the slow-acting; linv rvluy lit-ti tle nurgims.

Tn pmmrm'l, upon the unergization (if its linv ('l:t 1811. the! st t'mithny Switch N is 0;)- vmti-ti in tilt? :QHHI alumna!) as was this pri" intn Fulillt M, \t'lt'l'ti y connection l'lflltil tin-mini: lhv medium of the swittfik mg rvlny W5 and the wipers 190493. ini-lusivtz to an it'll0 trunk tern'iintiting in in opvmttn-n position assumed to he in this ('llht tlm trunk lino rcpt-wanted by bank ct ntilt-ts 1M 1 7. inclusive. The trunk confine tut-s 201 itlttl 2H2 extvnd by way nf normally t'ltlt-((l wintw-tii of win 207 to thc- (lollblewrmntl lt'l;l 2H \\'l|l.ll telzty is now EH01- gizvtl twin the Hill fll'lbfil l-i loop to complete I] lmltling tll'tllll for the primary and -Et' )llIl:t!' V linv switches M anti N which may llt it'tt ttl as follows: gmtmtl at ti nrmm littt 31H :mtl win-icing contact. nnrnnllly t'ltist l ltlliltfl'l 0? My K. t-mielurt'or J03, tent unltztvt 19.3. Ellltili't wipe-r llll anti armature itlil will ts u l'lqiiig mintm-t to Wllt innt'tim'i lt l. wiiwv lltv l'll'tlllt [livid-mm nun lmuit'h -it |lyin; gi'cinmi in tho lino MvitChitig 1'0 l t lHh t ilitililliliil it i ixm-gizzt-tl. while tilt: t'lllttl' llt'antt-h it tlw hill H :is tht' til'twinttslv tliN'l'illttl lmltiln; vim-nit n1" switthing relay ltil. It will lti' tilwmvvtl that from win, tttlttimz fllil :l l l'imt'h nf flu :thm'thnltiing lti'tllll wit-nth: in :ti-nmtm'v iii" of win 201 The inn l; (HIltlll til :u'mitttlrv 212" is mnm-t'twi in lilliilll it" with tho lmcl; i'UiiliGiS of LHI'IUF]liilttliligf 'lll'iililli'tH :Jlif" anti 212 of thv utltur twu it'ttllliwlttntllltltlllg in the same iwit lem. tln-i'vlay rvwlm'ing thew trunks hmy.

'hvn tin tlfllll' iU-VYUIHHl relay 2'05 is ent-rgimil, as has bean tlQSLFlbQd, a cirtuit is lit completed from ground G for lighting the signal lamp L. whereby the operator is informed that a call has been received. The operator will now operate momentarily the key K, associated with the lamp L. thereby completing in an obvious manner an energizing circuit for the relay 209. Upon energizing. the relay 209 locks itself to ground (i (Fig. *l) by way of conductor 214, e.\'- tinguisbes the lamp signal L. and extends the line conductors 201 and 202 to the 0perators telephone set.

The calling subscriber is now connected with the operator, to whom he repeats the telephone number of the subscriber at substation A". Upon learning the desired number the operator depresses in rapid successiontthe corresponding digit keys, shown at the right of Fig. 4. of the impulse transmitter associated with the trunk over which the call was received. and then depresses the starting button 3 of that impulse transmitter. The operator pays no further attention to the call after performing these operations.

In response to the actuation of-the digit keys certain ones of a plurality of levers (not shown) arranged radially on the wheel 231 are set by means of an arm (also not shown) operated by the magnet 227 and controlled by the solenoids 223. At the same time the lamp 1/ is lighted by the closme of contact springs 240. which are controlled mechanically by the operation of any one o the digit keys and which lock in operated position. In this way the required number is registered on the wheel 231. lhe lamp L indicates that the register is in set or partially set position but is not operating to transmit impulses.

Upon the operation of the starting hutton S the contact springs 240 are unlocked. thereby breaking the circuit of the lamp L. and at the same time a circuit is completed for the relay 225 which relay is accordingly energized with important results which will now be described. By the removal of ground G from conductor 214. the relay 209 is dcenergized to disconnect the operators head set. By the connection of ground G" to the conductor 215 a circuit is completed for relay 20G. Upon energizing. relay 5206 connects ground G" to the holding trunk conductor 203. in order to maintain the holding circuit closed independent of the relay 20S, and at the same time closes a circuit from the Janie 'ground G" to the relay 207. Relay 20?. upon energizing. disconnects the holding trunk conductor 203 from its multiple connection to armatures 212* and 212. whereby the other two trunks terminating in the same position are again placed in idle condition. As a further result of the energization of relay 307. a circuit is com plcted for the relay 131 of the relay group H, which may be traced as follows: ground at G, conductor 215, lower armature and contact of relay 206, lower armature and contact of relay 207, winding of relay 208, conductor 204, bank contact 196, wiper 192, lower armature and contact of relay 185. bank contact 176. wiper 17?. lower armature and contact of relay 161, conductor 1.312. and winding of relay 131' to battery B". Relay 208 included in the above circuit. operates the register R to count the call. Relay 131, upon energizing, completes the control circuit for the automatic selector switch which has already been prepared by the relay 207 and which may be traced as follows: ground at (F. lower winding of line relay 300, normally closed contact of relay 3052. terminal 1'27. conductor 154. spring 13.) and armature 137 of relay 130. spring 142 and armature 144 of relay 131. conductor 151. primary and secondary line switches M and N to conductor 202, inner lower armature and contact of relay "207, conductor .217. impulse springs E236. conductor 2m. inner upper armature and contact of relay .207. conductor 201. secondary and primary line switches N and M. conductor 150 armature 145 aml spring 143 of relay 131. armature 13R and spring H0 of relay 130. conductor 153.terminal 126. normally closed contact of relay 302. and the upper winding of line relay 300 to battery R More briefly described. the operation of relay 131 results in the substitution for the short-circniting conductor H1 of the loop extending back through the primary and secondary line switches M and and the contacts of the relay 207 to the impulse springs of the operators impulse sender. This operation. therefore. places the selector F. under the control of the said impulse springs.

A further result of the operation of relay 131 which should he mentioned at this time is the closure of a circuit for the relay 132. which circuit may be traced as follows: ground at G". armature 146 and its working contact. contact 156, spring 1-19. and winding of relay 132 to battery B". Upon energizing. relay 132 locks from ground on conductor 15.) by way of its armature H8. At its upper armature relay 1.32 prepares a short-circuiting path for relay 1210 which. however. is temporarily held open at the upper arlnature 1-17 of relay 131.

Returning now to Fig. 4. when the relay 22;) was energized as a result of the operation of'the starring button h it closed at its lower armature a circuit for the starting magnet 3:29 of the impulse sender. lpon energizing. the starting magnet :29 closes the contact springs 230 which are locked n'icchanically in closed position. A circuit is thereby completed for relay 1213 which relay. upon energizing. closes' at -2 upper armature a locking circuit for relay .25, and

at its lower armature opens the energizing circuit of magnet 21!). At the same time the lamp signal L- is' lighted in parallel with relay 220. A further result of the closure of springs 280 is thecompletion of the operating circuit of the motor 233 which now begins to rotate the wheel 231 and the impulse cam 23?, the geariin for driving the latter not being shown. The gears are so proportioned that. the cam '33? separates the impulse springs 23f) once for each lever (not shown) on the wheel 231 which passes the springs As soon as the first displaced lever arrives at the springs 232 the said springs are closed momentarily, thereby completing a circuit for the relay 234. Relay 234 closes in turn a circuit for the magnet 235 which operates to bring a pawl into engagement with the impulse cam. thereby stopping for a brief interval the operation of the motor. As soon as the relay 234; and the magnet 235 retract their armatures (they are made slow-acting by means of copper slugs on their cores) the motor again starts to revolve and another series of impulses is transmitted by the cam 237, the number of impulses being determined as before by the displaced lever on the wheel 231. It will be clear, therefore, that the impulse sender will operate to transmit in this manner as many series of impulses as there were digit keys depressed, the number of impulses in each series being determined by the displaced levers on wheel 23]. which levers it will be remembered correspond to the digit keys which were depressed.

Proceeding now to the operation of the automatic switches. the first series of impulses transmitted by the operators impulse sender serves to etl'ect the setting; ot the se lector E the operation being controlled over the previously described controlling circuit of the line relav 300. At each intcrrnption oi its ircuit the line rclav W is deen rgized momentarily and sends an i|upulse from ground G to the slow-acting rclav 303 and the vcrtical magnet fl0-l in series. The vertical magnet in response to those impulses. operates to step up thcswitch shaft until the wipers 320, 321. and 322 arrive at the horizontal level of haul; contacts in which are located the terminals oF trunlc\ extending to the desired connector group.

The rcla 303 the vcrti-al magnet and being shin-acting retain it armature during the series (it imulses. l p'on the. first upward movement; the haft the oll'-no|'n|ul springs 31] are l ed. lhcrclrv c mpleting a ircuit for the rot-Iv 1305 which extends from ground H in \:I\' ol' the armature and working coll tac ol' irl:1 105, and [he said oll-mn'mal spring to relay 130:3. l pon energizing. the

' tacts.

is energized in series with relay 305 locks itself ir endent of relay 303 at its upper armature and at its lower armature prepares a circuit for the rotary magnet 306 which is held, open during the vertical operation of the switch by the re la 303. At this point. it should be men tioned that b) the closure of the oft-normal springs 311 the line switching relay '302 was connected in series with the relay 305. The junction point 312,'however has already been connected to ground G as previously described so that the relay 302 is shortcirouited and remains inoperative. \Vhen the slow-acting relay 303 deenergizes at the end of the series of impulses it completes at its back contact the previously mentioned circuit of the rotary mag-net. 300. extendingfrom ground G Upon energizing, the. rotary magnet operates to rotate the 'ipers 320, 3-21, and 322 into engagement with the first set of bank contacts of the horizontal level opposite which they were raised. Near the end of its stroke the rotary magnet also breaks. at its upper armature, the loclv'ing circuit of relay 305; and at. its lower armature the circuit of the line switching rela v 302. Upon .detinergizing, the relay 30.) brealrs the energizing circuit of the rotary magnet which accordingly retracts its ar1nature to again close its upper and lower con The operation now depends on whether the first trunk line, the terminals of which are now engaged by the selector wipers, is busy or not. Assuming that. this trunk line is busy the test contact upon which the test or private wiper 321 is resting: will have ground potential upon it. which ground potential will serve to maintain the switching relay 302 short-cireuited and also to energize again the relay 305. The ro tary magnet circuit is therefore again completed and the same operation is repeated. It will be seen then that the relay 20:) will operate as an interrupter to step the switch wipers around through the medium of the rotary magnet as long as the test wiper 321 engages busy or grounded test. contacts. When a non-busy or nngroundcsl contact is reached aml the rotary magnet retracts its armature, the..jauction point 312 will no longer be grounded via the private wiper. whereupon the switching relay 302 will immediately energize in series with the relay 250.1. Relay 3012 is of such high resistance that rclav 305 remains imiperativc. liy the attraction oi its armature, the switching rehrv opens thc circuit of the release magnet to provide against the dehncrglzation ol" relays 300 and .301. shifts the private wiper .l'rom its normal connection to junction point ill}! to the holding conductor 155, and dis connects the line "()lllillt'ltll'm' lfiil and Hit l iom lhc line relay 300 and extends then] by way of the line wipers $130 and 322 bank till contacts 323 and 32:"). and conductors 370 and 372 to the double-wound relay 350 of the connector I.

The line relay 35H is :n-cordingly energized over the previously described controlling circuit extending back to the operator's impulse sender and upon attracting its armature. completes a circuit for the slowacting release relay 235i. l'pon energizing in turn. the relay 351 prepares a circuit for the vertical and rotary magnets 35!) and 360 in the usual manner and also conipletes a new holding circuit which maybe traced as follows: ground ti. contact and armature of relay 3.11. conductor Ili'l. bank contact H21, private wiper 32]. upper armature and working contact of relay 1H2 to wire junc tion ii-l. where the circuit divides. one branch extending by way of the winding of relay I302, (ill-normal contact 311. and the winding of relay 305 to the nngrounded pole of battery. and the other branch being the previously traced holding circuit. extending back to the primary and secondary tinder switches and I). it is understood that the above described holding circuit is completed before the slow-acting relay 301 of the selector E has bad time to deiinergize.

After the expiration of a brief interval the second series of impulses will begin coming in over the controlling circuit. Responsive to these interruptions the line relay arm dei nergizes a corresponding number of times and semis each time an impulse from ground at (1? to the slo\-a.cting relay 354 and the vertical magnet 35!) in series, side switch wiper 362 being in its first position. The vertical magnet. in response to these impul:-:cs. steps up the shaft until the wipers 2380. 381. and 382 stand opposite the horizontal level of bank contacts in which the line of substation A terminates. Relay 354. being slow-acting. retains its armature during the series of impulses and maintains a circuit from ground at G for the private magnet 357 and the wiper cut-oil relay 358 in parallel. At the end of the series of impulses. the relay 354- deiinergizcs and breaks the circuit of the private magnet. which latter controls the side switch wipers in the usual manner to advance them to their second position.

Ar'te another brief interval the third and final series of impulses will come in over the controlling circuit. resulting as before in de energizations of the line relay 350. Now. however. side switch wiper 36:! being in its second position. the line relay sends impulses to the slow actingrelay 354 in series with the rotary magnet 360. The rotary magnet operates in response to these impulses to rotate the wipers I380. 2581. and 38; until they rest. respectively. upon bank contacts 383. 384. and 385, these contacts forming the terminal of the line of substation A in the bank of connector F. The private magnet 3.3T and the wiper cutotl' relay 33h are energized during the series of impulses as before. the latter disconnecting the line wipers during rotation and the former, upon deenergizing. controlling the side switch wipers to advance them to their third position. it being assumed that the line ol sllb station A was idle when called.

As side switch wiper 3G3 comes into cngagemcnt with its third position contact point. a circuit is completed for the cut-off relay 414 of the called line as follows: ground at G. side switch wiper Still (in third position). wiper 558i. hank contact lli l. and winding of relay ill to battery l5. By the closure of the above circuit the cutoff relay 414 is operated to clear the line conductors +12 and +13 from their normal ground and battery connections. (lrouud at G also extends to multiples of bank con-- tact 384 in the banks of other connectors ol' the group. thereby making the line of substation .A busy to other calls.

By the engagement of side switch wipers 36+ and 365 with their third position contact points the connection between the calling and called substations is completed. relay 358 being deencrgized. lly the engagement of side switch wiper 36:! with its third position contact point, a circuit is completed for the ringing relay 356 in series with the interrupter 1, whereby ringing current is projected intermittently out. over the line of substation A to operate the signal in bridge thereof.

Returning now to the operatofis impulse sender (Fig. 4). after the transmission of the last series of impulses. the motor 23); continues to run until the wheel 2 -31 has made a complete revolution and returned to its starting point. Upon the return to normal the springs 230 are unlocked and allowed to separate. thereby stopping the motor 233. deencrgizing relay 221i. aml cxtiir guishing the lamp L. llelay 2213, by re tracting its armature. breaks the locking circuit of relay 225. which relay dcenergizes in turn to remove ground G from conductor 215. One result of this operation is the deencrgization of relay 206, which results in the opening of the circuit of relay ZUT and the removal of ground from the holding circuit ot' the primary and secondary line switches M and N. this latter operation resulting in the deenergization of the line switching relays in these line switches. A further result of the removal of ground from conductor 215 is the dei nergization of relay 131 of the relay group ll. llpon deencr gizing. relay 131 completes at its upper armature 147 a short circuit around relay 130. whereupon the said relay 130 also dei ner till fur :m

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HVPS

'rilu wllvL win. wii mn 2. In a telephone system, a plurality of subscribers lines, a plurality of primary and secondary finder switches for extending said lines when calling, starting circuits for each of said switches, means common to said primary finder switches for controlling said secondary finder switches and means common to said secondary finder switches for controlling said primary finder switches.

3. In a telephone system, lines divided into grou s, a plurality of line finder switches for eaci group for extending calling lines therein, a plurality of trunk finder switches for further extending lines in any group, a relay for each group of lines, a circuit controlled by each relay for starting an idle line finder, and a circuit controlled by said relays in common for starting an idle trunk finder.

4. In a telephone system, a plurality of suhscribeis' lines, a plurality of primary and secondary finder switches for extending said lines when calling, fixed and movable terminals in said finder switches for completing such extensions, each movable terminal being at all times in engagement with one of said fixed terminals, and means re.

sponsive to the initiation of a call for starting a primary and secondary finder simultaneously.

5. In a telephone system, a subseribers line, trunk lines, a progressively movable trunking switch for extending a connection from said subscrihers lineto any one of said trunk lines, an individual line relay for said line atthe exchangc,,means for partially operating said relay when the said line is calling, andmeans for completely energiz ing said relay when the said line is called.

6. In a telephone system, a subseribefis line, an individual line relay for said line at the exchange, said rela operable in two stages, a trunking switch or extending said line when calling, a circuit including said line for operating said relay through its first stage to provide for the extension of said line via said switch, and a second circuit completed after said switch has'operated for operating said relay through its second stage to open said first circuit.

7. In a telephone system, a siiibscribers line, a trunking switch for extending said line when calling, a circuit including said line for initiating the operation of said switch, a relay individual to said line and having a Winding in said circuit, contacts on said relay for opening said circuit, and means controlled by said switch for operating said relay.

8. In a telephone s stem, manual and automatic subscribers lines, automatic switches at the exchange for connecting calling and called lines of either kind, means for extending any calling line to one of said switches, an operators position, and means subscribers whereby the said calling line, if a manual line, is then automatically extended to the operators position.

5). In a telephone system, manual and automatic subscribers lines, an operators position, means for connecting a calling line with said operators position, and controlling means for said connecting means, said controlling means adapted'to discriminate between manual and automatic callinglines, whereby the former only are so extended.

10. In a telephone system, manual and automatic subscribers lilies, an operators position at the exchange, trunk lines, means for connecting calling lines of either kind with idlc trunk lines, an automatic trunking switch for each trunk line, and means in each trunk line responsive only to the connection of a manual calling line thereto for extending such trunk line to its associated automatic switch.

11.. In a telephone system, a trunk line having two branches, circuits of two different kinds, means for connecting any circuit with said trunk line, and discriminating switching means in said trunk line, whereby one kind of circuit is extended via one of said branches and the other kind of circuit is extcndcd via the other of said branches.

12.111 a telephone system, subscribcrs lines ot'l two kinds. an automatic switch, mcans for connecting any line when calling with said switch, a trunk line, and means actuated only when the calling line is of a particular kind for switching such calling linc from connection with said switch into connection with said trunk line.

13. In a tclcphonc system, subscribers lines of two kinds, an automatic switch. means for connecting any line when calling with said switch, a trunk linc, means actuated only when the calling line is of a particular kind for switching such calling line from connection with said switch into conncction with said trunk line. and an opcrntor's position in which said trunk linc tcrminutes.

14. In a telephone systcm, subscribers lincs of two kinds, an automatic switch. means for (ohm-cling any linc when calling with said switch. a trunk line. means actuatcdonly when the railing line is of a particular kind for switching such calling line from connection with said switch into connection with said trunk linc, an opcratm-s position in which said trunk linc lcrminatcs, an impulse lransmiltcr, mcans for connccling it with said trunk linc, and means for switching said trunk line from conncction with said calling line into conncction with said switch, whereby said switch may be controlled by said transmitter.

15. In a telephone system, subscribers lines of two kinds, an automatic'switch, means for connecting any line when calling ing a calling line to said trunk, and means associated with the calling line for initiating the operation of said automatic selecting mechanism.

27. In a telephone system, subscribers lines, a trunk line provided with selecting nn-chanism, other trunk lines in groups, an automatic switch for extending a calling line to said first trunk line, means whereby the calling subscriber may control a portion of said mechanism to select a desired one of said groups of trunk lines, another group of trunk lines, automatic means for controlling another portion of said mechanism to select a trunk in said other group, and means individual to the calling line for initiating the operation of said automatic means,

28. In a telephone system, a plurality of subscribers lines, a plurality of primary and .-ccomlary finder switches for extending said lines when calling, a switching relay in each finder. a relay for sinulltal'ieously starting a primary and secondary finder responsive to a all, and means for thereafter simultaneously energizing the associated switching relays.

25;. in a telephone system, a plurality of subscribers lines. a plurality of primary and secondary finder switches for extending said lines when calling, starting circuits for each of said switches. a relay common to said primary finder switches for controlling said secondary finder switches and a relay common to said sccomlary finder switches for controlling said primary finder switches.

30. In a telephone system, a plurality oi subscribers lines, a plurality of line finder switches controlled from said lines for finding any one of said lincs. a plurality of trunk finder switches for finding any one of said line finders. said trunk finders controlled also from said lines. whereby a connection may be established from any one of said lines to one of said line finders and through one of said trunk finders to another line.

31. In a telephone system, a plurality of lines, a relay common to said lines. a plurality of line finders, a plurality of trunk finders. said relay controlled from said lines. said line and trunk finders controlled by said rclay, the line finders to find the lines and the trunk finders to find the line finders.

3:2. in a telephone system, a plurality of subscribers" lines. a plurality of line finder switches controlled from any one of said lines for finding any one of said lines, a plu rality of trunk finder switches for finding anyone olsaid linc finders, said trunk finders controlled also from any one of said lines, whereby a conncction may he established from any one of said lines to one or' said linc finders and through one of said trunk finders to another line.

83. In a telephone system, a plurality of lines, a relay common to said lines, a plurality of line finders, a plurality of trunk finders, said relay controlled from any one of said lines, said line and trunk finders controlled by said relay. the line finders to find the lines and the trunk finders to find the line finders.

EH. In a telephone system, a plurality of subscribers lines, a plurality of primary and secondary finder switches for extending said lines when calling, a switching relay in each finder, a relay for simultaneously starting a primary and secondary finder responsive to a call, means for thereafter simultaneously energizing the associated switching relays, each finder having a wiper and a bank with a line terminal for each line with means for moving said wiper into engagement with any one of said terminals to find a line, each of said trunk finders having a wiper and a. bank of terminals one for each line finder, and means for moving its wiper into engagement with any one of the line finder terminals to make the connection with a line finder.

35. In a telephone system, a plurality of subscribers lines, a plurality of primary and secondary finder switches for extending said lines when calling, starting circuits'for each of said switches, a relay common to said primary finder switches for cont olling said secondary finder switches and a relay common to said secondary finder switches for controlling said primary finder switches, each finder having a wiper and a bank with a line terminal for each line with means for moving said wiper into engagement with any one of said terminals to find a line, each of said trunk finders having a wiper and a bank of terminals one for each line finder, and means for moving its wiper into engagement with any one of the line finder terminals to make the connection with a line finder.

ill. In a telephone system, manual and automatic subscribers lines, automatic Switches at: the exchange for connecting calling and called lines of either kind, subscriber controlled means for extending any calling line to one of said switches, an operator's position, and electromagpetic means whercby the said calling line, it a manual line. is then automatically extended to the opcratofs position.

37. In a telephone system, manual and automatic suhscribers lines, an operators position at the exchange, trunk lines, means for connecting calling lines of ther kind with idle trunk lines. an autonmtic trunking switch for each trunk line, and a relay in each trunk line responsive only to the connection of a manual calling line thereto For.

extending such trunk line to its associated automatic switch. I

88. In a telephone system, manual and an lim, a lrunliing switch fur extending; said him when calling, a circuit iiirludmg mid line for initiating the upuratiun ml mill switch, a relay indiiidual to said Hus; a winding of aid rulay included iii said lllH riivuii Wl'ulPljrj said allay 11?. 1 in; 1-. 1'girmr1i iii: LL'UYLL ("Jlliflir 1111 said i'e-lay Em m ni ml ling a plurality :l' druid- (iii ill rliifs living: illi' sai-l llli; l'liilllii, iii ins; ('llfil li j izr waui will; rtuuhii lwl hWiiKlh said i'rla 1 upiei al iiiurii'ruil wlu-ii PFHS' 40. I11 a lelvpliuiir l imaiir ;-'ul1sr.t1ihi -r iinvs :11: uprsifimu means for i mnwr .11 mu iii 1 1' with said Upil'l'ilflli posil ion and mail roliiugg' mums fur said connecting 115611118 said wat rolling mnans having a relay ih{)lh'l'-i\i3 only to fli manual line equipn'iem, \Yliiflvlrk said connecting means is operated in igmmwi only manual lines to the nperamra p isitiua,

21. In a telephone systma, manual and an. tmnafiv subscribers lines, an 0;, sitimi :il llur-xrlmngy, ljiu'nli ii: for cnmievting calling lines in uillw-r iciu'l with irlla trunk lines. an autnmatin timid ing swilrli for ath trunk liar, and imam in Hu'll trunk lira rispnnsi i In lw mguipnwn? i-vl' a lHHlHitiii wal 11, m nding sun-l1 trunk lilii i; 11 aul'ommir -zwiti'li, lioriahy illfllihi Milling against the automatic lines -19. In a telephnn :v s sbem, a trunkliun having two branches. calling Cir-suits w an difi rrm'st kinds. means for ,uinirtliug; any one (if said rir uifs with said trunk Him, and automatic disrr minating. switching 11mins in said trunk line, wlwreby' one kind ml win unit is extended via 0111 of said branches and ihv other kind of circuit is exlaudorl via ilu: other of said ln-aunhes.

-43. In a ftlQPllOHQ sysimn. subsvrilwrw lines of two kinds, an aidmi'ialir switi'li, means for cmmvrting any one (if said liiws when calling with s: id switvli, a trunk iiuiu and auloumtiv moans artuafod wily lu'u lhv railing line is a partivuiar kind for \V1l(1lllllgt|lkl| calling ine from immuulimi will; said su'ilvli into rumumtion Willi said lruni; lim'.

1.! la a i zlupluma y r 111 sulwfiilim s liar-s of liwu kinds an :uitmnatic switch, 2111 11115 fm cunruajitiug any 011i: 0% said lines rrlm: railing will; said t-3\-\il li. a lirunli lime, ruiimualiii mmns acliilaird only when H19 wi ling linv is; of a iart iculair liiud i'nr -uilrl1iug such walling line flag-m aimuectinu with said switch into (Hill'lifillflil with said trunk linv, and an (11101211111 j 1f)$'.ll]lltll in. which said dunk line tiirziiinar as.

"i5" 111 a, irluplmuu simn, suiisrribars Elm-s 0f iwzi kinds, i111 autuii ivvilwsli, means fur i-uiinwling any 0111-. pl iil li'w's Wiliil railing Willi said svvilirg iffl, ii'uuli aiduuru'ii- Ha ms (111 mm wily iiM: Film ."aifii illi-(r i :1, mil sail-w nk; wiiiil iuiiimg' liniwit :1. in; said adiiilizl i i i lim inf r Hawaii-011 with :T; i said swituli may bi: (IUliliUlliii in said iisinitlifii. i

45. In :1. leluplmnu sysiiim s is-irril'a-rs liiws ff two kinds, an aul'm'aativ w-iilzrrli, uu aais for 00111101361253 any 011a of said lines wliwi willing with said switch, a iJlHll I linei aid-um: 'iil'IJ-P. actuafwl only when i'hc [ailing H111 is if a parll-walar lilfli for 1 il flimg siuj'li calling line rm'n minim fimi "m -aifiuu iii i 1 t F i and trim: uni ueriaman iiillili swans ii)! lag ii iruuli: Zimu Iikinlir fur swi'elvliing v rimr iina i'mm wiuumtiuia with said (ff-vii a liar: 111111 iroimur'tion with said swirls 1i irviw DISCLAIMER.

1,308.553.-llinfrcrl T. Pow-e71, Chicago, Ill. 'li-znernonnExemmen SYSTEM. Patent dated July I, 1919. Disclaimer liled April 15, 1927, by the assignee by mesne assignments, .lufmnnfic [Chef/"ir- Inc.

Hereby enters a disclaimer to claims 8, 9, 22, 25, 26, 36, 38, 40, and 47 in said specification, which are in the following words, to wit:

8. In a telephone system, manual and automatic subscribers lines, automatic. switches at the exchange. for connecting calling and called lines of either kind, means for extending any calling line to one of said switches, an operators position, and means whereby the said calling line, if a manual line, is then automatically extended to the operators position. I

9. In a telephone system, manual and automatic subscribers lines, an operator's position, means for connecting a calling line with said operator's position, and controlling means for said connecting means, said controlling means adapted to discriminate between manual and automatic calling lines, whereby the former only are so extended.

2:2. In a telephone system, a trunk line having a normally open branch, circuits of different electrical cha'acter, means for connecting any circuit with said trunk line, and switching means dependent on the electrical characteristics of a connected circuit for closing said branch.

25. In a telephone system, subscribers lines, a trunk line extending to an operators position, means for connecting a calling line with said trunk line, means associated with certain of said lines for bringing about the operation of said con necting means, and means associated with certain other of said lines for preventing the operation of said connecting means.

26. In a telephone system, subscribers lines, a trunk line provided with directively controlled selecting mechanism and automatic selecting mechanism, either of said mechanisms being operable independent of the operation of the other, means for extending a calling line to said trunk, and means associated with the calling line for initiating the operation of said automatic selecting mechanism.

36. In a telephone system, manual and automatic subscribers lines, automatic switches at the exchange for connecting calling and called lines of either kind, subscriber controlled means for extending any calling line to one of said switches, an operators position, and electromagnetic means whereby the said calling line if a manual line, is then automatically extended to the operators position.

38. In a telephone system, manual and automatic subscribers lines, an operator's position, automatic switching mechanism common to a plurality of said subscribers lines for connecting a calling line with said operators position, a relay for con trolling said switching mechanism, said relay adapted to be operated when the calling line is a manual line. and ino 'ierative when the calling line is an automatic line, whereby the former only are extended to said operators position.

it). In a telephone system. manual and automatic subscribers lines, an operators position, means for connecting one of said lines with said operator's position. and controlling means for said connecting means, said controlling means having a relay responsive to the manual line equipment, whereby said connecting means is operated to connect only manual lines to the opcratofis position.

$7. In a telephone system. a trunk line having a normally open branch. circuits of different electrical character. means for connecting any one of said circuits with said trunk line. and automatic switching means dependent on the electrical characteristics of a connected circuit for closing said branch.

[Official Gazette May 0', 1927'. l 

